A serologic examination of the blood for syphilis is included in every complete study of a patient. In cases in which there are indications of disease of the central nervous system, the spinal fluid also is tested. This report deals with the Kahn reactions of blister serum and their comparison with the reactions of blood and of spinal fluid.
When serologic tests are used to aid in the detection of syphilis, blood usually is chosen for the study, although there are other fluids which may be examined, e. g., gastric contents, cerebrospinal fluid and blister serum. Since tests of the blood may be negative in cases in which tests of the cerebrospinal fluid are positive, and vice versa, it was interesting to compare the reactions of these fluids with the reactions of a third. If the reactions of blister serum were found to be comparable to the reactions